The Periods

1. Period is the horizontal rows of elements in the Periodic Table.
2. The modern periodic table has 7 periods.
3. The period number indicates the number of electron shell.
4. Elements in the same period have same number of electron shells.
5. The proton number of elements increases from left to right crossing the period.
6. The number of electrons is also increases from left to right crossing the period.

Lanthanide and Actinide Series

1. The sixth period has 32 elements. Due to short of space, 14 elements in the transition metal group are removed from the same horizontal row and is placed below the main table, These elements are called the Lanthanide Series.
2. The seven period also has 32 elements. With the same reason, 14 elements are removed from the same horizontal row and is placed below the main table, These elements are called the Actinide Series.